Approach scouting with a scrutinizing eye, experts say

Bean leaf beetles and other leaf defoliators are showing up in substantial numbers in soybean fields across the Corn Belt.

Now is a crucial time to scout fields for these pests, according to entomologist Ron Hammond of The Ohio State University Extension and Phillip Glogoza, University of Minnesota Extension crops educator. According to Hammond, not only bean leaf beetles, but other defoliators including Japanese beetles and grasshoppers are being found in fields throughout Ohio.

Scouting these pests requires an acute eye for specific insect traits, he says.

"When scouting for soybean defoliators, you want to focus on two things. First, you have to scout randomly across the entire field and not just confine your scouting to field edges," Hammond says. "Japanese beetles and bean leaf beetles tend to feed across the field, while grasshoppers are normally found at field edges.

"Secondly, don't get fooled into thinking, if heavy feeding is found on top of the plant canopy, that the whole plant is infested. Japanese beetles and bean leaf beetles tend to confine themselves to just the upper plant leaves. Make sure that 15% defoliation is true for the entire plant before applying treatments," he says.

This upper-plant feeding of bean leaf beetles has been observed in many fields around Minnesota, according to Glogoza. Despite the sometimes high severity of this type of leaf-feeding, Glogoza says more comprehensive sampling reveals a less severe problem, underscoring the need for a scrutinizing eye when scouting fields.

"A few fields were reported to have great enough populations [last week], that sparked some interest. Leaf feeding in the tops of plants is very visible," Glogoza says. "Sweep net sampling at these sites indicated bean leaf beetle infestations in the range of 0.2 beetles per sweep to a high of 1.6 beetles per sweep. Though not serious infestations, we can see that some of these sites are close to treatable levels."

Also key to determining fields in which a grower may encounter high bean leaf beetle populations is assessing the characteristics of the land, Glogoza says, as well as the timing of spring planting.

"[Fields with near-treatable levels] were within half a mile of the Red River and other heavily wooded sites," he says. "These locations would be ideal overwintering sites for the beetles. Also, the largest populations were in the first planted fields in the area. The beetles are attracted to the first beans to emerge in the spring."

Bean leaf beetles and other leaf defoliators are showing up in substantial numbers in soybean fields across the Corn Belt.